The Medical Letter on Drugs and Therapeutics
COVID-19 Update: New Pfizer and Moderna Vaccine Formulations for 2023-2024
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Med Lett Drugs Ther. 2023 Oct 16;65(1687):167-8   doi:10.58347/tml.2023.1687c
Principal Faculty
  • Mark Abramowicz, M.D., President has disclosed no relevant financial relationships.
  • Jean-Marie Pflomm, Pharm.D., Editor in Chief has disclosed no relevant financial relationships.
  • Brinda M. Shah, Pharm.D., Consulting Editor has disclosed no relevant financial relationships.
Additional Contributor(s)
  • Michael Viscusi, Pharm.D., Associate Editor has disclosed no relevant financial relationships.
Upon completion of this activity, the participant will be able to:
  1. Review the recommendations for use of the updated 2023-2024 mRNA COVID-19 vaccines.
 Select a term to see related articles  Comirnaty   COVID-19   RSV   Spikevax   vaccines 
Revised 10/23/23: Table 1 has been updated.

New 2023-2024 formulations of the mRNA COVID-19 vaccines manufactured by Pfizer/BioNTech (Comirnaty) and Moderna (Spikevax) that more closely target currently circulating variants have been licensed by the FDA for use in persons ≥12 years old and made available under FDA Emergency Use Authorizations (EUAs) for use in persons 6 months to 11 years old. The bivalent (original and Omicron BA.4/5) formulations of the Pfizer and Moderna vaccines are no longer authorized for use in the US.1-3

THE NEW VACCINES – The new formulations are monovalent vaccines that code for the spike protein of the XBB.1.5 Omicron strain of SARS-CoV-2.

EFFICACY – No clinical studies evaluating the effectiveness of the new vaccine formulations are available. Licensure and authorization of both vaccines were based on safety and efficacy data with previous formulations of the vaccines and on immunogenicity data showing that the neutralization potency of the new formulations against currently circulating strains of the virus, including XBB.1.5, EG.5 (Eris), FL.1.5.1 (Fornax), and BA.2.86 (Pirola), is similar to that of previous formulations against the SARS-CoV-2 strains that they targeted.1,4,5

ADVERSE EFFECTS — Adverse effects of earlier versions of the mRNA COVID-19 vaccines have included injection-site reactions, fatigue, irritability, fever, chills, muscle and joint pain, headache, vomiting, decreased appetite, and lymphadenopathy. Severe allergic reactions and Guillain-Barré syndrome have been reported. Myocarditis and pericarditis can occur; the incidence is highest in adolescent and young adult males.6

DOSAGE RECOMMENDATIONS – Generally, persons ≥5 years old should receive a single dose of a 2023-2024 vaccine formulation ≥2 months after their previous COVID-19 vaccine dose. Children 6 months to 4 years old who have already received ≥2 Pfizer or Moderna vaccine doses should receive a single dose of the corresponding 2023-2024 vaccine ≥8 weeks (Pfizer) or ≥2 months (Moderna) after their most recent dose. Those 6 months to 4 years old who received <2 previous doses should be given additional doses until they have received 3 total doses of the Pfizer vaccine or 2 total doses of the Moderna vaccine. Children 6 months to 11 years old with immunocompromise (solid-organ transplant recipients and equivalent) should receive at least 3 total age-appropriate COVID-19 vaccine doses, including at least 1 dose of a 2023-2024 formulation. Dosage recommendations for the updated vaccine formulations are summarized in Table 1.2,3

CDC RECOMMENDATIONS – The CDC recommends that all persons ≥6 months old receive either of the two 2023-2024 mRNA COVID-19 vaccines.7


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